docs: def warningFlag(self):
          '''
          When viewing individual event registrations, there are a large number of potential
          issues that can arise that may warrant scrutiny. This property just checks all of
          these conditions and indicates if anything is amiss so that the template need not
          check each of these conditions individually repeatedly.
          '''
          if not hasattr(self,'invoice'):
              return True
          if apps.is_installed('danceschool.financial'):
              '''
              If the financial app is installed, then we can also check additional
              properties set by that app to ensure that there are no inconsistencies
              '''
              if self.invoice.revenueNotYetReceived != 0 or self.invoice.revenueMismatch:
                  return True
          return (
              self.priceWithDiscount != self.invoice.total or
              self.invoice.unpaid or self.invoice.outstandingBalance != 0
          )